# [GRASS-user] compute path with a maximum slope

Stefan Blumentrath Stefan.Blumentrath at nina.no
Tue Dec 10 02:54:44 PST 2019

```Hi,

you can either try r.walk (https://grass.osgeo.org/grass78/manuals/r.walk.html) and modify variable according to Your threshold or you set slope values above your maximum to NULL (e.g. r.mapcalc expression="slope_below_max=if(slope>37.5,null(),slope)") and then use r.cost (https://grass.osgeo.org/grass78/manuals/r.cost.html, NULL ("NoData") are not traversed by the algorithm).

Cheers,
Stefan
GRASS GIS manual: r.walk<https://grass.osgeo.org/grass78/manuals/r.walk.html>
DESCRIPTION r.walk computes anisotropic cumulative cost of moving between different geographic locations on an input elevation raster map whose cell category values represent elevation combined with an input raster map layer whose cell values represent friction cost.. r.walk outputs 1) a raster map showing the lowest cumulative cost (time) of moving between each cell and the user-specified ...
grass.osgeo.org

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Sendt: tirsdag 10. desember 2019 10:34
Til: grass-user at lists.osgeo.org <grass-user at lists.osgeo.org>
Emne: [GRASS-user] compute path with a maximum slope

I have a DEM in grass using a proj that is in UTM. Viewshed, slope, etc
work fine. What I want to do is have grass compute a path between two
points such that the slope doesn't exceed a maximum value. I don't care

I suspect there is some guide on the internet for this problem, but
just can't compose the right question for a search engine. A link would
be appreciated. If not, some basic guidance would be helpful.
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